In a weathering apparatus, the weather-dependent aging behaviour of a sample, in particular of a flat material sample, is assessed, with the sample being subjected to artificial weathering. The weathering apparatus for this purpose normally has a weathering chamber, in which holding means are arranged for holding samples to be weathered, and in which one or more radiation sources are arranged in order to apply radiation, in particular UV radiation, to the samples.
Apparatuses for artificial weathering of material samples are generally used to estimate the life of materials which are continuously subjected to natural weather conditions during their use, and which thus deteriorate under climatic influences such as sunlight, solar heat, humidity and the like. In order to obtain a good simulation of the natural weathering characteristics, it is advantageous for the spectral energy distribution of the light produced in the apparatus to correspond as far as possible to that of the natural solar radiation, for which reason appliances such as these use xenon emitters as their radiation source. In addition, an accelerated ageing test of the materials is achieved essentially by illuminating the samples more intensively than the natural conditions, thus speeding up the ageing of the samples. A statement about the long-term ageing behaviour of a material sample can thus be made after a relatively short time.
The majority of the material samples which are investigated in artificial weathering appliances are composed of polymer materials. The weather-dependent deterioration of polymer materials is caused substantially by the UV component of the solar radiation. The primary photochemical processes which take place in this case, that is to say the absorption of photons and the production of stimulated states or free radicals, are not dependent on the temperature. In contrast, the subsequent reaction steps with the polymers or additives may be dependent on the temperature, so that the observed ageing of the materials is likewise dependent on the temperature.
One or more UV radiation sources, such as xenon radiation sources, is or are optionally used in the previously known weathering apparatuses. As is known, these allow the entire solar spectrum to be simulated quite well, in which case the relatively high spectral component in the infrared spectral range can be attenuated by suitable IR filters.
The radiation power emitted from the UV radiation sources is measured by UV sensors, in which case it is possible to provide for each UV radiation source to have its own associated UV sensor. The output signal from the UV sensors is supplied to a control and recording device in which the UV radiation powers can be recorded during a weathering process. Furthermore, the output signals from the UV sensors can be supplied to a control device, by means of which the electrical power to be supplied to the power supply devices for the UV radiation sources can be regulated at constant UV radiation power levels.
It is known for broadband UV sensors to be used in weathering apparatuses, which have a sensitivity range in the range from 300 nm to 400 nm, in accordance with the IS Standard. However, there is also frequently a requirement for weathering processes to be carried out with the UV radiation power being measured using the NB Standard. In this Standard, the radiation power is optionally measured in the two narrowband ranges of 340 nm ±10 nm or 420±10 nm, with the latter range being outside the UV range, in the visible, blue spectral range. However, in the prior art, there are only sensors which are calibrated for in each case one of the already mentioned three sensitivity ranges. Accordingly, if there is a wish to use a different standard for the radiation power measurement from one weathering process to the next, in particular based on a different sensitivity range, then it is either necessary to replace the sensors or, if this is not possible, a different weathering apparatus must be used.
A change in the Standard for the measurement of the radiation power is accordingly associated with considerable effort and additional costs in the prior art.